In recent years, researches have been actively made into a light-emitting device which uses, as illuminating light, fluorescence that a light-emitting section containing a fluorescent body generates in response to an excitation light beam emitted from a semiconductor light emitting element such as a light emitting diode (LED) or a semiconductor laser (LD: Laser Diode).
A technique related to such a light-emitting device is exemplified by light-emitting devices disclosed in Patent Literatures 1 through 4.
Patent Literature 1 allows a vehicle headlamp having variable lighting characteristics to be mechanically simply structured and improves obstacle resistance and response speed. Patent Literature 2 discloses a headlight which, while restraining an enlargement, is capable of (i) reducing electric power consumption and (ii) forming desired density in a light-distribution pattern. Patent Literature 3 discloses a vehicle lamp capable of electrically switching between a horizontally wide light-distribution pattern and a light-distribution pattern suitable for AFS (Adaptive Front-lighting System) casting light beams leftward and rightward. Patent Literature 4 discloses a light source device which prevents a device from getting large-sized, increasing in weight, and getting high in manufacturing cost even in the light source device equipped with a function of varying light distribution.
In other words, the techniques of Patent Literatures 1 through 4 can also be as described below.
The vehicle headlamp of Patent Literature 1 includes a plurality of laser elements, a light collecting lens which collects light emitted from the respective plurality of laser elements, and a drive electronic circuit which causes the plurality of laser elements to selectively emit light. This allows lighting characteristics of the vehicle headlamp to comply with a running drive condition and an ambient condition.
The headlight of Patent Literature 2 includes an emission unit which emits, by performing scanning, light from a respective plurality of laser elements in accordance with a determined light-distribution pattern. This allows formation of a desired light-distribution pattern. Further, since this headlight includes an output adjusting section which adjusts respective outputs of the plurality of laser elements, density can be formed in a light-distribution pattern.
Note that Patent Literatures 1 and 2 disclose that the plurality of laser elements may be replaced with a plurality of LEDs.
According to the vehicle lamp of Patent Literature 3, a projection lens and a horizontally long surface light source including a plurality of LEDs are disposed so that respective optical axes thereof are inclined by a given angle with respect to an axis extending in a front-to-rear direction of a vehicle. According to this, in a case where an LED on the outer side than a focal point of the projection lens is on, the horizontally wide light-distribution pattern is realized. Meanwhile, in a case where an LED on the inner side than the focal point of the projection lens is on, the light-distribution pattern suitable for AFS (Adaptive Front-lighting System) casting light beams leftward and rightward can be realized. Namely, it is possible to switch between the foregoing two light-distribution patterns.
The light source device of Patent Literature 4 includes light control means for changing an emission range and/or a light intensity distribution of an excitation light beam emitted from a solid light source to a fluorescent body. This allows a light distribution to be variable by a simple method.